Supralittoral Research Articles

Coral conglomerate platforms as foundations for low-lying, reef islands in the French Polynesia (central south Pacific): New insights into the timing and mode of formation

In French Polynesia, low-lying, reef islands, composed of unconsolidated skeletal material rest on cemented conglomerate platforms. These are regarded as mainly generated by storm activity during the mid-late Holocene. Field observations and coral sampling were carried out on conglomerates from three atolls located in the north-western Tuamotu, namely, Takapoto, Takaroa and Fakarava. There, fifty-seven samples were dated using the uranium‑thorium (U/Th) method. The lateral age distribution of clasts indicates that conglomerate platforms have accreted from lagoon sides seawards.In addition to U/Th dating, the coral clast-age datasets include eighteen calibrated radiocarbon ages from Takopoto and other Tuamotu atolls – Takapoto, Mataiva, Rangiroa, Arutua, Apataki, Marokau, Hao, Pukarua, Nukutavake. As a matter of comparison, another seventy-seven, previously published radiometric conglomerate ages from various French Polynesian islands (Society, Tuamotu, Gambier) were incorporated in the present study. It appears that the formation of conglomerate platforms has taken place principally during a 2000-year interval, between 3000 and 1000 yr BP when sea level dropped from about +0.60 m to its present position. Before and after these periods, lower amounts of coral detritus have been provided to conglomerates, possibly due to clast deposition in adjacent lagoons and to trapping into reef rim-islands respectively.Age discrepancies of most coral clasts collected from multiple stacked layers at Takapoto and Fakarava do not exceed 500 years, strongly suggesting limited clast reworking before final stabilization. The superimposition of two to four firmly cemented conglomeratic layers at the same place gives evidence that marine cementation has operated shortly after clast deposition. This event is regarded as having taken place within both phreatic and vadose environments. Rubble sheets found seawards at some atoll-rim sites are interpreted to be conglomerates in the making, emplaced over the last centuries.Dating of atoll-islet material indicates clearly that, over the 2500–1000 yr-BP span, the building of conglomerates and overlying islets has interplayed. The former have evolved within subtidal to supratidal zones while the latter have been accreted subaerially. This may explain the firmly consolidated state of platforms and the unconsolidated state of islets. Due to their firmness, conglomerate platforms are assumed to be key structures for the maintenance of atoll islands subjected to sea level rise and increasing storminess in the coming centuries.

Effect of long term natural weathering on oil composition: study of the 41-years-old Amoco Cadiz and 20-years-old Erika oil spills

On 16 March 1978, the oil tanker the Amoco Cadiz, transporting 223,000 tons of crude oil and 4,000 tons of bunker fuel oil, suffered a failure of her steering mechanism and ran aground on Portsall Rocks, on the Breton coast. The entire cargo spilled out as the breakers split the vessel in two, progressively polluting 360 km of French shoreline from Brest to Saint Brieuc. This was the largest oil spill caused by a tanker grounding ever recorded in the world. The consequences of this accident were significant, and it caused the French Government to revise its oil response plan (the Polmar Plan), to acquire equipment stocks (Polmar stockpiles), to impose traffic lanes in the Channel and to create Cedre. On 12 December 1999, the tanker Erika broke up and sank off the coast of Brittany (France) leading to the spill of 20,000 tons of a heavy fuel oil. 400 km of the French Atlantic coastline were polluted. Because of the characteristics of the oil (a very heavy fuel oil with a high content of light cracking oil) and the severe weather conditions (a centennial storm with spring tides) when the oil came on shore, the Erika spill was one of the most severe accidental releases of oil along the French coastlines. All types of habitat were concerned, and pollution reached the supratidal zone affecting terrestrial vegetation and lichens. In 2019, respectively 41 years and 20 years after these major oil spills affecting the French shoreline, a sampling round was conducted at two sites recorded to present some residual traces of oil. Samples of weathered oil were collected, extracted with methylene chloride and then purified through an alumina-silica microcolumn. SARA fractionation and GC-MS analyses were performed in order to assess respectively the total degradation of the weathered oil (amount of saturates, aromatics and polar fraction) and the specific degradation of nalkanes from n-C9 to n-C40, biomarkers (such as terpanes, hopanes and steranes) and PAHs (parents and alkylated derivatives).

Hypersaline tidal flats as important “blue carbon” systems: a case study from three ecosystems

Abstract. Hypersaline tidal flats (HTFs) are coastal ecosystems with freshwater deficits often occurring in arid or semi-arid regions near mangrove supratidal zones with no major fluvial contributions. Here, we estimate that organic carbon (OC), total nitrogen (TN) and total phosphorus (TP) were buried at rates averaging 21 (±6), 1.7 (±0.3) and 1.4 (±0.3) gm-2yr-1, respectively, during the previous century in three contrasting HTF systems, one in Brazil (eutrophic) and two in Australia (oligotrophic). Although these rates are lower than those from nearby mangrove, saltmarsh and seagrass systems, the importance of HTFs as sinks for OC, TN and TP may be significant given their extensive coverage. Despite the measured short-term variability between net air–saltpan CO2 influx and emission estimates found during the dry and wet season in the Brazilian HTF, the only site with seasonal CO2 flux measurements, the OC sedimentary profiles over several decades suggest efficient OC burial at all sites. Indeed, the stable isotopes of OC and TN (δ13C and δ15N) along with C:N ratios show that microphytobenthos are the major source of the buried OC in these HTFs. Our findings highlight a previously unquantified carbon as well as a nutrient sink and suggest that coastal HTF ecosystems could be included in the emerging blue carbon framework.

Crude oil biodegradation in upper and supratidal seashores

The salinity of the upper parts of seashores can become higher than seawater due to evaporation between tidal inundations. Such hypersaline ecosystems, where the salinity can reach up to eight-fold higher than that of seawater (30–35 g/L), can be contaminated by oil spills. Here we investigate whether such an increase has inhibitory effects on oil biodegradation. Seawater was evaporated to a concentrated brine and added to fresh seawater to generate high salinity microcosms. Artificially weathered Hibernia crude oil was added, and biodegradation was followed for 76 days. First-order rate constants (k) for the biodegradation of GC-detectable hydrocarbons showed that the hydrocarbonoclastic activity was substantially inhibited at high salt – k decreased by ~75% at 90 g/L salts and ~90% at 160 g/L salts. This inhibition was greatest for the alkanes, although it extended to all classes of compounds measured, with the smallest effect on four-ring aromatics (e.g., chrysenes). Genera of well-known aerobic hydrocarbonoclastic bacteria were only identified at 30 g/L salts in the presence of oil, and only a few halophilic Archaea showed a slight enrichment at higher salt concentrations. These results indicate that biodegradation of spilled oil will likely be slowed in supratidal ecosystems and suggest that occasional irrigation of oiled supratidal zones could be a useful supporting strategy to remediation processes.

An alternative approach to delineate wetland influence zone of a tropical intertidal mudflat using geo-information technology

Mudflats are important tropical coastal wetlands having high carbon sequestration and biodiversity potentials. The actual reach of a mudflat environment spreads far beyond its perennial wetland areas in a coastal site. Accurate demarcation of the extent of these buffer areas is imperative for sustainable wetland management. This study tried to delineate the wetland influence zone (WIZ) of an intertidal mudflat in the Medinipur coastal plain, India as a functional extension around the considerably smaller yet hydrous cum muddy depressions. Normalized Difference Water Index (NDWI), derived from Sentinel-2 MultiSpectral Instrument (MSI) datasets, and Temperature Vegetation Dryness Index (TVDI), derived from the coupled use of Sentinel-2 MSI and Landsat-8 datasets, had been analyzed and merged to develop nine characteristic zones. Among these, eight zones (Zone I to Zone VIII) were identified as part of the WIZ and the rest one (NDWI: < −0.15, TVDI > 0.7) was considered as a supra-tidal zone, devoid of the mudflat features. Although the overall extent of WIZ (Minimum: 339.20 ha, Maximum: 350.22 ha) did not change much from 2016 to 2020, the inter-zonal spatial arrangements of vegetation and physiography transformed continuously. The gradual disappearance of the major tidal creek from the south-western parts and increasing human footprints throughout the mudflat had expedited this transformation. Accordingly, periodic assessments incorporating microwave and optical datasets along with high precision in-situ measurements of soil moisture was suggested for the efficient monitoring of these fragile tropical ecosystems.

Quantifying seasonal variations in microphytobenthos biomass on estuarine tidal flats using Sentinel-1/2 data.

Quantifying temporal and spatial changes in microphytobenthos (MPB) biomass is critical for understanding its ecological function in estuarine food web networks and carbon flows. However, tidal fluctuations and the complex composition of coastal sediment limit remote sensing applications for estimating MPB biomass seasonal variations in estuarine tidal flats. We integrated radar Sentinel-1 (S1) and optical Sentinel-2 (S2) remote sensing data to quantify the temporal and spatial variability in MPB biomass in the Changjiang estuary, China. Pixels of water bodies on the tidal flats were removed by dynamic threshold segmentation of the water index with the combined S1 and S2 data, and salt marsh pixels were masked with the first red-edge band in the S2 data. We used the continuum-removed spectral absorption depth feature to construct a regression model for estimating MPB biomass with a regression coefficient of 0.81. The results showed that spectral absorption continuum removal methods using broadband multispectral data for MPB estimation are a promising alternative to hyperspectral narrowband ratio operation. Compared with the widely used normalized difference vegetation index (NDVI), the scaled absorption depth feature was more stable for MPB estimation under a changeable sediment background. The produced seasonal map showed that the high biomass levels of the MPB in the study area are not limited to one season and one site, with an annual mean biomass of 14.39mg chlorophyll a (Chl-a)·m-2 and 71% confirmed accuracy. The highest biomass levels occurred in summer in the supratidal zone (19.51mg Chl-a·m-2) and in spring in the intertidal zone (17.10mg Chl-a·m-2) in the Changjiang estuary. The relative shore height, derived from the tidal range here, is an important variable that shapes the MPB spatial distribution. This study demonstrates the potential of integrating high-spatial-resolution (10m) S1 and S2 data for future large-scale estimation of intertidal MPB.

Contamination of Heavy Metals, Polychlorinated Dibenzo-p-Dioxins/Furans and Dioxin-Like Polychlorinated Biphenyls in Wharf Roach Ligia spp. In Japanese Intertidal and Supratidal Zones

We investigated the pollution levels of 6 heavy metals and 29 dioxins (polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (DL-PCBs)) in intertidal and supratidal zones by using wharf roaches (Ligia spp.) collected from 12 sampling sites on the coast of Northeast Japan from November 2011 to June 2012. The total concentrations of heavy metals ranged from 177 to 377 µg/g-dry weight (dw), and the predominant metals were copper, zinc, and aluminum. The order of the detected level of heavy metals was zinc &gt; aluminum &gt; copper &gt; cadmium &gt; lead &gt; chromium, and this trend was similar to a previous report. The total toxic equivalent (TEQ) value of the PCDD/Fs ranged from less than the limit of detection (&lt;LOD) to 2.33 pg-TEQ/g-dw, and the predominant congener was octachlorodibenzodioxin (&lt;LOD to 110 pg/g-dw). Compared with PCDD/Fs, DL-PCBs were detected at a predominantly higher level (total TEQ value: 0.64–27.79 pg-TEQ/g-dw). Detected levels of dioxins, especially DL-PCBs in the wharf roach, were like those in the bivalves. These results indicate that the wharf roach could reflect heavy metals and dioxin pollution in the supratidal zones and is a suitable environmental indicator for these environmental pollutants. This is the first study to investigate heavy metals, PCDD/Fs, and DL-PCBs pollution in coastal isopods in Japan.

Discovering symbiosis in the supralittoral: bacterial metabarcoding analysis from the hepatopancreas of Orchestia and Tylos (Crustacea)

Herein, we investigated for the first time the microbiota from the hepatopancreas of the talitrid amphipod Orchestia montagui and the oniscidean isopod Tylos ponticus, two crustacean species associated with beached leaves of the seagrass Posidonia oceanica (Posidonia banquette). We carried out a metabarcoding analysis based on several hypervariable regions of the bacterial 16S rRNA gene. At the same time, three representative habitats of the supralittoral zone, namely leaf surface of Posidonia banquette, sandy shore and surface seawater were examined by means of bacterial metabarcoding analysis. Our data analyses indicated that the bacterial microbiota from the hepatopancreas and that from the marine habitats form distinct groups in terms of the taxonomic composition. Comparative analyses revealed that some bacteria were associated with the hepatopancreas of the syntopic O. montagui and T. ponticus but were not detected in the supralittoral habitats. This suggests that distinct components of the microbial community may be uniquely adapted within the hepatopancreas. The microbiota from the hepatopancreas of O. montagui was more complex than that of T. ponticus. However, the putative presence of polysaccharide-degrading bacteria in both species indicated symbiotic microbiomes that might be involved in the functionality of the hepatopancreas. A deeper understanding of halophilic hepatopancreatic symbionts in the supralittoral zone also has broad relevance to applied research, particularly to the biotechnological sector related to marine biomass conversion.

Patterns of Body Shape Diversity and Evolution in Intertidal and Subtidal Lineages of Combtooth Blennies (Blenniidae).

Marine intertidal zones can be harsher and more dynamic than bordering subtidal zones, with extreme and temporally variable turbulence, water velocity, salinity, temperature, and dissolved oxygen levels. Contrasting environmental conditions and ecological opportunities in subtidal versus intertidal habitats may generate differing patterns of morphological diversity. In this study we used phylogenetic comparative methods, measurements of body length, and two-dimensional landmarks to characterize body shape and size diversity in combtooth blennies (Ovalentaria: Blenniidae) and test for differences in morphological diversity between intertidal, subtidal, and supralittoral zones. We found that subtidal combtooth blennies have significantly higher body shape disparity and occupy a region of morphospace three times larger than intertidal lineages. The intertidal morphospace was almost entirely contained within the subtidal morphospace, showing that intertidal combtooth blennies did not evolve unique body shapes. We found no significant differences in body size disparity between tidal zones, no correlations between body shape and tidal zone or body size and tidal zone, and no body shape convergence associated with tidal zone. Our findings suggest that a subset of combtooth blenny body shapes are suitable for life in both subtidal and intertidal habitats. Many species in regions of morphospace unique to subtidal combtooth blennies exhibit distinct microhabitat use, which suggests subtidal environments promoted morphological diversification via evolutionary microhabitat transitions. In contrast, limited intertidal body shape diversity may be due to strong selective pressures that constrained body shape evolution and environmental filtering that prevented colonization of intertidal zones by certain subtidal body shapes.

A latest Cretaceous gastropod fauna from the Jiaolai Basin of East Asia

A non-marine gastropod fauna from the continuous uppermost Campanian to Maastrichtian deposits of the Jiaolai Basin (eastern North China) was studied. Four species attributed to four genera and an undetermined species were described, including Truncatella jiaozhouensis sp. nov., ?Pomatiopsidae gen. et sp. indet., ?Hydrobia datangensis Yü, 1977, Valvata jiaolaiensis sp. nov., and Physa sp. Among them, two new species were established. The finding of ?Hydrobia datangensis is consistent with a Late Cretaceous age as previously inferred from the charophyte flora. Available sedimentological data of the gastropod-bearing beds combined with a gastropod taphonomical study suggest that all five species lived in shallow lakes, whereas ?Pomatiopsidae gen. et sp. indet. also inhabited floodplains. Furthermore, extant Truncatella species are either fully terrestrial or dwell amphibiously in the supralittoral zone in temperate to tropical regions, usually close to the water line, as well as near freshwater of river estuaries. Therefore, Truncatella jiaozhouensis sp. nov. supposedly has lived in the surrounding shorelines of the shallow lake.

Correlation between Polycyclic Aromatic Hydrocarbons in Wharf Roach (Ligia spp.) and Environmental Components of the Intertidal and Supralittoral Zone along the Japanese Coast.

Polycyclic aromatic hydrocarbon (PAH) concentrations in wharf roach (Ligia spp.), as an environmental indicator, and in environmental components of the intertidal and supralittoral zones were determined, and the PAH exposure pathways in wharf roach were estimated. Wharf roaches, mussels, and environmental media (water, soil and sand, and drifting seaweed) were collected from 12 sites in Japan along coastal areas of the Sea of Japan. PAH concentrations in wharf roaches were higher than those in mussels (median total of 15 PAHs: 48.5 and 39.9 ng/g-dry weight (dw), respectively) except for samples from Ishikawa (wharf roach: 47.9 ng/g-dw; mussel: 132 ng/g-dw). The highest total PAH concentration in wharf roach was from Akita (96.0 ng/g-dw), followed by a sample from Niigata (85.2 ng/g-dw). Diagnostic ratio analysis showed that nearly all PAHs in soil and sand were of petrogenic origin. Based on a correlation analysis of PAH concentrations between wharf roach and the environmental components, wharf roach exposure to three- and four-ring PAHs was likely from food (drifting seaweed) and from soil and sand, whereas exposure to four- and five-ring PAHs was from several environmental components. These findings suggest that the wharf roach can be used to monitor PAH pollution in the supralittoral zone and in the intertidal zone.

Historic dispersal barriers determine genetic structure and connectivity in a supratidal sandy-beach brooder

The supralittoral zones of sandy beaches are particularly vulnerable to coastal development and other activities that cause localised habitat destruction. Supratidal species, such as peracarid crustaceans, which lack a pelagic larval phase and tend to avoid direct contact with the swash, are therefore expected to be distributed as isolated populations, with implications for their long-term survival. Genetic population structure of one such species, the pill bug Tylos capensis, was investigated based on mitochondrial cytochrome c oxidase subunit I (COI) haplotype sequences, to assess demographic history and regional population connectivity in the presence of potential dispersal barriers (an estuary, coastal cliffs) along the Indian Ocean coast of South Africa. Here, pill bugs demonstrated strong and significant genetic structure at the regional scale, with 3 distinct clades across the species’ geographic distribution. At a localised spatial scale, coastal cliffs intersecting the high shore appeared to be a strong barrier to gene flow between adjacent populations, while a permanently open estuary did not limit gene flow. Estimates of historic gene flow and patterns of COI differentiation coincided with greater habitat continuity during the Pleistocene glaciations at sea levels between -75 and -120 m, when the African south coast was probably dominated by sandy beaches. While gene flow among low-dispersing pill bug populations is unlikely to benefit from a network of closely spaced coastal protected areas, the isolated nature of this species, coupled with the cryptic diversity inherent in this taxon, emphasizes the need for their protection. The importance of protecting the intact littoral active zone of beaches is highlighted.

Flora of cyanobacteria from rocky supralittoral zone of the Meganom peninsula (The Black Sea)

Complete lists of biota are the scientific foundation on which studies of the regional biological diversity are based. Considering the emergence of a new classification scheme of cyanoprokaryotes, there is a need to revise the species composition of Cyanobacteria of various biotopes. The article describes the flora of Cyanobacteria of the Meganom Peninsula (eastern Crimea). Taking into account the latest nomenclature-taxonomic changes, 44 species of Cyanobacteria were listed for the supralittoral zone of the protected area of the peninsula. Species are representatives of 23 genera, 15 families, 5 orders and 2 subclasses. A fifth part of the species list consists of rare and endangered species that need protection. A complex of the leading species of the marine supralittoral zone of the Meganom Peninsula was identified; species, which are indicators of saprobity, were determined, and the algal community saprobity index was calculated (S = 0,9). The supralittoral microalgoflora is characterized by the predominance of attached benthic species and complex of marine and brackish-water forms. The prevalence of cosmopolitans and wide-range boreal-tropical species highlight the azonality of the biotope of the marine rocky supralittoral zone.

Middle Holocene Coastal Environmental and Climate Change on the Southern Coast of Korea

We obtained a 15 m drill core from Deukryang Bay on the southwest coast of Korea, which is now an area of reclaimed land used for agriculture. We investigated changes in the depositional environment and hydrological climate responses to sea level changes using sedimentary facies, radiocarbon ages, grain-size analysis, total organic carbon (TOC), total sulfur (TS), and stable carbon isotopes (δ13C). Sediment deposition began at 12,000 cal yr BP and was divided into four stages based on changes from fluvial to intertidal environments related to Holocene marine transgression events. Stage 1 (&gt;10,000 cal yr BP) is represented by fluvial sediments; Stage 2 (10,000–7080 cal yr BP) is represented by the deposition of mud facies in an intertidal zone in response to sea level rise; Stage 3 (7080–3300 cal yr BP) was a period of gradually descending sea level following the Holocene maximum sea level and is characterized by gradual changes in TOC, TS, and C/S ratios compared with the mud facies of Stage 2. Stage 4 (3300 to present) was deposited in a supratidal zone and contains low TS and an abundance of TOC. Based on our TS and C/S ratio results, the south coast of Korea was mainly affected by sea level rise between 7000 and 3000 cal yr BP, during the middle Holocene. At 3000 cal yr BP, sea level began to stabilize or gradually decrease. In addition, changes in δ13C values are clearly observed since ca. 5000 cal yr BP, in particular, large hydrological changes via freshwater input are confirmed in 4000–3000 cal yr BP. We consider these shifts in freshwater input indicators of an increased influence of El Niño and La Niña conditions, related to the weakening of the East Asian Summer Monsoon (EASM) and changes in sea surface temperature (SST) of the Western Pacific Ocean during the middle Holocene climatic optimum (between 7800 and 5000 cal yr BP). The cooling periods of SST in East Asia between 8400 and 6600 cal yr BP reported from the west coast of Korea are related closely to changes in vegetation (as evidenced by δ13C) from 7700 cal yrs BP to the present in the southwest coast of Korea. We interpret the freshwater input events at 4000–3000 cal yr BP to be related to changes in SST in response to the weakening of the EASM on the southwest coast of Korea. However, additional research is needed to study the southward migration effect of the westerly jet related to SST and atmospheric circulation controlling terrestrial climate in the middle Holocene.

Sedimentary Dynamic and Composition of a Tidal Channel in a Tropical Hot Semi-Arid Environment, NE Brazil

Tidal channels comprise a peculiar and dynamic environment. This paper aims to recognize the sedimentary distribution and composition of a tidal channel located in a semi-arid climate area in order to understand the sedimentary dynamics of the region. This region has economic and environmental importance considering that several activities are developed in the area such as; salt industry and aquaculture with shrimp farming. The results and discussion presented here on the Barra Grande Port tidal channel are based on 43 superficial samples distributed in the area, in which we analyzed the grain-size distribution and the calcium carbonate and organic matter contents. The data enabled the characterization and compartmentalization of the tidal channel on five sections and the interpretation of the sedimentary dynamics of the area. The sections present an important variation in the composition and selection. The section 1 is located in supratidal zone while sections 02, 03, 04 and 05 are in intertidal zone. The grain-size mean has a tendency to decrease toward the end of the channel as well as the gravel percentage, and the carbonate and organic matter contents. Differently, the mud content and the sorting increase toward the end of the channel and the skewness becomes more positive. In a general way, the carbonate content is high throughout the tidal channel ranging from 20 to 98% while the organic matter content is low ranging from 0 to 3%. This sedimentary distribution occurs due to the development of a hydraulic dam on section 3, causing a morphological growth of this sand bar, which acts as a natural hydraulic dam, hampering the access of the tide and consequently reducing the effectiveness of the transport, resulting in the deposition of fine sediments in the sheltered areas of the channel (sections 04 and 05). The high temperatures and low rainfall of the tropical hot semi-arid climate allowed the development of carbonate sedimentation as well as the development of anthropic activities such as salt extraction in artificial salt pans which may have influenced the low levels of organic matter.

Distribution of Carbon and Nitrogen as Indictors of Environmental Significance in Coastal Sediments of Weizhou Island, Beibu Gulf

Carbon and nitrogen contents and their isotopic components, and AMS (Accelerator Mass Spectrometry) radiocarbon dating ages, were measured for 57 coastal sediments from Weizhou Island to analyze the distribution of total inorganic carbon (TIC) and its carbon and oxygen isotopic components (δ13Ccarb and δ18Ocarb), total organic carbon (TOC) and total nitrogen (TN) contents and their stable isotopic components (δ13CTOC and δ15NTN), and their environmental significance. The results showed that the oldest age of coastal sediments on Weizhou Island was 2750 cal. a BP (before present), and the average TIC contents of cores A1, A2, B1, C1, and D1 in the intertidal zone were all greater than 5%, where δ13Ccarb and δ18Ocarb were enriched, whereas the TIC contents in cores A3, C2, and D2 of the supra-tidal zone were low, where δ13Ccarb and δ18Ocarb were depleted. Moreover, TIC decreased sharply, 4.95% on average, to close to zero from the estuary to the upstream region in the C1-C2 section. The average C/N ratio was 7.02, and δ13CTOC and δ15NTN were between −14.96‰ and −27.26‰ and −14.38‰ and 4.12‰, respectively. These measurements indicate that the TIC in coastal sediments mainly came from seawater. Cores A1, A2, and B1 in the northern intertidal zone exhibited organic terrestrial signals because of C3 and C4 plant inputs, which indicates that the important source on the northern coast of Weizhou Island came from island land but followed the decrease in C3 plants. The lacustrine facies deposits were mainly distributed in the upper reaches of the river, the northern coastline was advancing toward the sea, and part of the southwestern coastal sediments rapidly accumulated on the shore under the influence of a storm surge. The relative sea level of the Weizhou Island area has continuously declined at a rate of approximately 2.07 mm/a, using beach rock as a marker, since the Holocene.

Supratidal existence drives phenotypic divergence, but not speciation, in tropical rocky-shore snails

AbstractThe mechanisms underlying the evolutionary adaptation of animals that transcend the ecological barrier separating the intertidal and supratidal zones of rocky shores are poorly understood. Different wetting frequencies in these zones in tropical regions (daily vs. seasonally, respectively) impose different physical stressors, which should drive phenotypic variation and ultimately speciation in the animals that inhabit them. We studied morphological, physiological and genetic variation in a tropical high-shore gastropod that transcends these zones [Echinolittorina malaccana (Philippi, 1847)]. Variation in melanization, shell features and evaporative water loss was linked to regular seawater wetting, frequent activity and feeding, and solar exposure in intertidal snails, and to inactivity and prolonged aestivation in the shade during continuous air exposure in supratidal snails. Despite selective pressure for phenotypic divergence, and reproductive isolation of the populations in either zone, their mitochondrial COI gene sequences confirmed that they represent a single species. Speciation in our study case is probably constrained by the limitation on activity, mating and reproduction of supratidal snails, such that their populations can only be sustained through intertidal pelagic larval recruitment. Comparisons with other studies suggest that supratidal speciation and specialization for life in this zone probably require moderation of the abiotic (desiccative) conditions, to facilitate greater activity and interaction of animals during air exposure.

Salinity controls soil microbial community structure and function in coastal estuarine wetlands.

Soil salinity acts as a critical environmental filter on microbial communities, but the consequences for microbial diversity and biogeochemical processes are poorly understood. Here, we characterized soil bacterial communities and microbial functional genes in a coastal estuarine wetland ecosystem across a gradient (~5 km) ranging from oligohaline to hypersaline habitats by applying the PCR-amplified 16S rRNA (rRNA) genes sequencing and microarray-based GeoChip 5.0 respectively. Results showed that saline soils in marine intertidal and supratidal zone exhibited higher bacterial richness and Faith's phylogenetic diversity than that in the freshwater-affected habitats. The relative abundance of taxa assigned to Gammaproteobacteria, Bacteroidetes and Firmicutes was higher with increasing salinity, while those affiliated with Acidobacteria, Chloroflexi and Cyanobacteria were more prevalent in wetland soils with low salinity. The phylogenetic inferences demonstrated the deterministic role of salinity filtering on the bacterial community assembly processes. The abundance of most functional genes involved in carbon degradation and nitrogen cycling correlated negatively with salinity, except for the hzo gene, suggesting a critical role of the anammox process in tidal affected zones. Overall, the salinity filtering effect shapes the soil bacterial community composition, and soil salinity act as a critical inhibitor in the soil biogeochemical processes in estuary ecosystems.

Pore structure response of sedimentary cycle in coal-bearing strata and implications for independent superposed coalbed methane systems

ABSTRACT Coalbed methane (CBM)-bearing systems are often superposed in coal-bearing strata with multiple coal seams. The formation and development of independent superposed CBM-bearing systems is based on the vertical variation of pore structure in coal-bearing strata. This study examines the potential of the pore structure cycle of the intervening rock formation in coal-bearing strata that compartmentalize the CBM system, which, in turn, assist in the production of the coal gas. The pore structure is characterized using lithology, sequence stratigraphy, and mercury injection porosimetry data generated from 25 samples of the intervening formation. The samples originate from a representative drilling operation located in the Bide-Santang basin, western Guizhou, China. We divided the pore structures into 4 types (I, II, III and IV): type I, “well sorted and fine slanting degrees;” type II, “well sorted and coarse slanting degrees with extremely low mercury saturation;” type III, “poorly sorted and uniform distribution” and type IV, “poorly sorted and polarization of micropores and macropores.” Pore structure changes cyclically in accordance with the sedimentary cycle: pores developed poorly within rocks that formed in deep water bodies with low energy and reducing sedimentary environments, such as lagoons and limited subtidal and mire facies; pores are better developed within rocks formed in shallow water bodies with high energy and oxidizing environments, such as supratidal flats, intertidal zones, and distributary channel facies. Third-order sequence boundaries (SB) favor the development of secondary porosity, whereas the maximum flooding surface (MFS) possesses a superior condition for forming regional impermeable barriers between different CBM-bearing systems. The sequence stratigraphic framework limits the variation trend of the pore structure and therefore limits the vertical distribution of independent superposed CBM-bearing systems. The findings are of great significance for enriching the geological theory of multi-seam CBM accumulation, optimizing the co-mining methods and improving the co-mining efficiency of superposed CBM systems.

Selective microbial-induced biomineralization of a siliciclastic zoned coastline in a constricted modern tidal flat, Kuwait (Northern Arabian Gulf)

At Ras Kadhma embayment (north Kuwait), fabrics such as micrite envelopes, calcified microbial filaments, and micritic grain-to-grain bridges are observed in this modern sabkha environment in Kuwait Bay, associated with a tripartite facies classification. Three tidal zones were delineated by 8 vertical core samples, each marked by laterally diachronous units with different lithofacies and biofacies. Microbial populations (Lyngbya and Schizothrix), living within a distinct differentiated intertidal flat zone, were identified and their effects on sediments recorded. The extreme salinity, temperature, and chemical gradients in the shoreline environment have contributed to a microbial ecosystem that is trapping, binding, and biologically inducing CaCO3 precipitation, producing a variety of sedimentary structures now conventionally regarded as MISS (microbially induced sedimentary structures). The microbial fabrics are preserved in aggregates within the intertidal to the continental vadose zone. Core samples and outcrops were collected and analyzed mineralogically, chemically, and microbiologically. Field mapping on a meter scale reveals a concentric zonation, subtidal, intertidal, and supratidal zones, distinguished by textural and biological differences. Distinct lithofacies reveal varying stages of biomineralization with optimum conditions developed in the intertidal and lagoon sediments enhanced by microbial populations. The results of the study contribute to the understanding of the complex interaction between microorganism forming mats, the tidal flat sediments, and the physical parameters that control this setting in Kadhma Bay. Recurring colonization of these siliciclastic sediments in the intertidal zone will be permanently terminated in the coming decades by advancing intertidal sand bars resulting from the destruction of the Tigris-Euphrates delta.